AES128 Encryption Library

[Kaveh.M]

I am using my nRF52833 chip to send 20 bytes beacons frequently. 

I want to encrypt the initial 16bits of my data using AES128. 

What is the library to use for this purpose? How to include the initialization vector and encryption key? 

Thanks

[Kaveh.M]

There already seems to be some examples in SDK for AES encryption under examples\crypto\nrf_crypto\aes

What is the difference between these examples aes_all_cli, aes_cbc_mac, aes_cbc_with_padding, aes_ccm, aes_ctr. 

[Vidar Berg]

They all use the AES cipher; the difference is in what mode of operation they support. I think this wiki article explains the differences pretty well: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation 

SDK documentation: AES Example

[Kaveh.M]

Thanks Vidar. I am going to use aes_cbc_mac library and encrypt my beacon. 

How much is the expected added power consumption and delay to my code because of this AES128 encryption of beacon data? 

[Vidar Berg]

The impact of encryption on your average current consumption will depend on how long it takes to encrypt the payload and how frequently you update the data. I don't think there will be a very noticeable difference, but this is something you have to verify with your application.

[Kaveh.M]

Thanks Vidar. I do encryption of first 16bytes of data in my beacon every 10 sec and send the beacon. 

I read somewhere that the encryption speed on a computer CPU typically is in order of Gb per sec. What is the clock frequency of internal CPU in nRF52833 so that I can scale this number. I use external crystal at 32.7k Hz on XL1 and XL2 pins.